CHEMISTRY COMMUNITY

Shanzey

Why is the anode in the solution with a lower molarity? Is it because electrons from the cathode solution diffuse through the porous membrane to enter the anode solution?

Shanzey

How does temperature affect rate constant k? Does an increase in temperature cause an increase in the rate constant?

Shanzey

How are we able to tell whether or not something is an elementary reaction? Also how is writing the rate law of an elementary reaction different from a non-elementary reaction?

Shanzey

I liked drawing Lewis structures!

Shanzey

In the solutions manual, it mentions that a catalyst provides a completely different reaction pathway. Is this different pathway due to the lowered activation energy?

Shanzey

Does anyone understand the last question on the Q&A PowerPoint that Dr. Lavelle posted? I don't understand how you are able to determine the rate limiting step.

Shanzey

What does the A value in the Arrhenius equation mean? Also when do we use this equation?

Shanzey

How are you able to tell which reaction is the slow step? Is the equilibrium reaction usually the slow step?

Shanzey

On the constants and equations sheet, one of the formulas is k= A exp(-Ea/RT) and another formula is lnK= -(Ea/RT) + lnA. Are these two formulas the same thing, except the first one has done e to the power of each term to cancel out the natural logs (ln)?

Shanzey

What is the difference between rate constant and rate? Does the rate constant of a reaction never change, while the rate is subject to change due to changes in molar concentrations?

Shanzey

For part c, I understand that increasing the product or reactant concentration does not change the equilibrium constant, but does an increase in reactant cause an increase in the rate constant? Are these two concepts related?

Shanzey

How are you able to tell the units for k? Also, why do the units for k change depending on the order of the reaction?

Shanzey

Why don't concentrations for zero order reactions matter?

Shanzey

How are we able to tell the order of a reaction, and how do we know whether to use integrated or differential rate laws?

Shanzey

For 7A.15, how do we know which experiments for C to use when finding the orders for A and B (since none of the C experiments remain constant as the other two change)?

Shanzey

When writing the half reactions, why don't we include the given H+ proton for our oxidation half reaction? Is this because the solution is acidic, so we ignore the extraneous H+ in the equation given?

Shanzey

For 6N.5 part a, how do we determine the charges of the atoms in the compound Hg2Cl2?

Shanzey

For part 6M.11a, we are asked to draw the cell diagram with the given information: Co2+/Co and Ti3+/Ti2+. How are we able to determine the states of matter of these elements based off of the information given? Both Ti and Co are transition metals, so I thought they would both be solids; however, onl...

Shanzey

For the graph, why are the increase in I2 production and the decrease in I production curved rather than linear? Why would these rates change at a curved/exponential rate, rather than constant?

Shanzey

For 6L.7c, the solution uses Ni(s) as the electrode for the cathode in the cell diagram, but Ni(s) is neither a reactant or product of the reduction half reaction. Why do we have to use Ni(s)? Is it because Ni is already present in the solution/reaction and can act as a metal conductor? Would using ...

Shanzey

For part 6L.5d, the solutions manual splits two half reactions while including Au(s) in both half reactions. Why do we need to have a solid in each half reaction? Can we not have half reactions with just aqueous substances, thus causing us to have the solids in both half reactions?

Shanzey

The question asks us to write the balanced half reactions for potassium permanganate and iron(II) chloride; however, in the solutions manual, the steps to work out the problem do not include potassium or chlorine. Is this because they are spectator ions? Also, is this because it is in an acidic solu...

Shanzey

STP means standard temperature and pressure, during which the pressure is 1atm and temperature is 273K (or 0 degrees Celcius).

Shanzey

How does the reaction quotient affect our value for E in the Nernst equation? Does having a larger reaction quotient result in a smaller or larger value for E? Also, what is going on conceptually when this occurs?

Shanzey

Is Gibbs free energy only related to E using the equation (delta)G^o = -nFE^o? In addition, does the spontaneity of a reaction affect E?

Shanzey

In lecture today, Dr. Lavelle mentioned that there are some problems in the textbook where we have to tell what is wrong with a given cell diagram. One of the things that can be wrong with the cell diagram is the putting the anode (oxidation reaction) on the right. How are we supposed to be able to ...

Shanzey

I am having trouble understanding salt bridges. How do they work, and why are they needed? Do they make batteries last longer?

Shanzey

For acidic reactions, we have to add water to the reduction and oxidation reactions to balance out the oxygens. Do we have to add water to balance oxygens in basic conditions, or do we only add OH- to balance oxygen molecules?

Shanzey

How can you tell the difference between what is reduced and what is oxidized? Is it only dependent on proton transfer?

Shanzey

Will we have to memorize all of the charges of all of the elements, or just the ones that are in the most common groups (such as Groups 1, 2, 16, 17, etc.)? Is the only way to tell the charge of transition metals by seeing the whole compound the element is in?

Shanzey

How do we tell the charge of Mg in MgO4-? Is it because oxygen normally has a charge of -2, and the total compound is -1, thus causing us to determine that Mg has a charge of +7?

Shanzey

How are you able to tell what the charge what of each element is? Do all of the charges cancel each other out to make each side of the reaction neutral?

Shanzey

How do we know when to use the lnQ equation or the lnK equation? Is it dependent on whether the system is in equilibrium or not?

Shanzey

What is the difference between (delta)G and (delta)G^o in the equation (delta)G = (delta)G^o + RTlnQ?

Shanzey

Does standard entropy of a reaction depend on the state of a molecule? For instance, would the standard reaction entropy of liquid water be different from that of water as a gas?

Shanzey

Does having more moles of a molecule mean increased entropy? For instance, would 5 moles of H2O would have a higher entropy compared to 1 mole of H2O?

Shanzey

In the formula for standard reaction entropy, why is is S(products) and S(reactants) at standard conditions, rather than (delta)S(products) and (delta)S(reactants)? Are we looking at residual entropies, rather than the change in entropies?

Shanzey

In lecture during Monday of week 4, Dr. Lavelle did an example of a neutralization reaction. When he did the question, he used the Q= mC(delta)T equation, which I understand; however, he used 100g as his mass for the equation. In order to find the mass, did he add the 50ml of each solution and then ...

Shanzey

On the constants and equations sheet, there is an equation for calculating just internal energy: U=(3/2)nRT. When do we need to use this equation? Were there any questions using this in the homework?

Shanzey

I don't really understand what Gibbs free energy is conceptually, and how it is related to enthalpy and entropy. I understand that, by looking at the equation, an increase in enthalpy increases Gibbs free energy and an increase in entropy decreases Gibbs free energy, but why is that?

Shanzey

Why do reversible expansions do more work than irreversible expansions? Does it have to do with constant or changing pressure?

Shanzey

Are these two concepts related? Are they opposites of each other, or are they two completely separate things?

Shanzey

Why does NO2 having more atoms give it a higher molar heat capacity compared to NO? The solutions manual says that it is because NO2 has more bonds to absorb added energy, but I am not really sure of what this means.

Shanzey

For part b, why is the heat positive? I thought that the energy (186.0 kJ) would be negative, because we are looking at the reverse reaction that forms N2.

Shanzey

For this question, why do we treat mass of the calorimeter as m= 1g? Why is the mass of the calorimeter not taken into account for solving the problem?

Shanzey

For question 4A.1b, why is coolant in a refrigerator coil a closed system? Also, for 4A.1f, why is a living plant an open system?

Shanzey

What is the difference between heat capacity and specific heat capacity? Is it a matter of whether they are intensive or extensive properties?

Shanzey

In the method 3 example done during lecture, were the values used to calculate (delta)H(rxn) standard/given values, or do we have to calculate them using a formula?

Shanzey

I do not really understand the difference between standard reaction enthalpy and standard enthalpy of formation. What makes them different, and how would we be asked to use them?

Shanzey

If method 2 is the least accurate method for calculating the net enthalpy change, would we ever be asked to use it, or should we just understand it conceptually and know why it is inaccurate?

Shanzey

When calculating this such as the enthalpy of vaporization or sublimation, will the enthalpies for the physical states (such as H(vapor) and H(liquid) for vaporization) be given to us, or is there some formula for how to calculate these values?

Shanzey

I know Dr. Lavelle went into quite a bit of depth as to why steam causes burns worse than boiling water, but I am still a bit confused. Why does this occur? In my notes, I wrote that steam has a large enthalpy of condensation: is that the reason why?

Shanzey

I understand that enthalpy is a state property (meaning that only the current state determines its value), but why aren't the intermediary states taken into account?

Shanzey

How do we know when to use the PV=nRT equation? Do we just use it to calculate initial concentration for pressure before creating our ICE table? Were there any homework questions that showed us an example of when/how to use it? Also, do the units for pressure (bars vs. atm) matter when using this eq...

Shanzey

For part c, how are we able to tell which reaction is more thermodynamically stable? Does it have to do with whether we would get more monatomic molecules or diatomic molecules for the reactions, and them comparing the K values of each equation?

Shanzey

When approximating, how do we test to make sure that our approximation violates the 5% rule? Do we have to do (equilibrium concentration)/(initial concentration)?

Shanzey

I am a little confused as to what the significance of Le Chatelier's Principle is. Is it applicable to all chemical reactions?

Shanzey

Are pressure and volume inversely related to each other? If the pressure of a system doubled, would the volume halve?

Shanzey

How does an increase in temperature affect exothermic reactions differently from endothermic reactions? If you apply heat, does the endothermic reaction favor formation of products, and does the exothermic reaction favor the formation of reactants?

Shanzey

For part c, why does the ratio of P(O2)/P(O3) change between the two experiments? I understand that the equilibrium constant K= (P(O2)^3/P(O3)^2) does not change, but why would the ratio P(O2)/P(O3) based off of the amount of moles present?

Shanzey

How do we know when to use Kc or when to use Kp? Does it need to be specified which we are using, or do we have to assume that Kp applies to things in the gas phase (since it deals with partial pressure), while Kc typically is used for aqueous solutions?

Shanzey

I know that it was touched upon in lecture, but I am still having trouble with this concept. Why don't solids and liquids affect the value of K?

Shanzey

I understand that at equilibrium the rates at which the reactions occur are equal, but is the equilibrium constant K the rate at which these reaction occur? In addition, how can you speed up the rate at which a reaction occurs?

Shanzey

What is the difference between the equilibrium constant K and the reaction quotient Q? Does K remain constant, while Q is subject to change?

Shanzey

How do we know when to use an ICE table to find the composition of the mixture, or when we have to use only the K=[products]/[reactants] equation? Is it dependent on whether initial concentrations or equilibrium concentrations are given?

Shanzey

Based off of that, how would you determine the pH for each of those scenarios?

Shanzey

What is the difference between amphoteric and amphiprotic compounds? Why is something that is amphiprotic also amphoteric, but not the other way around?

Shanzey

Under acidic conditions, when pH is higher than the pkA, why is the acid protonated as HA? In addition, when the pH is higher than the pkA, why does the solution become more basic and give off an H+ to form A-?

Shanzey

If you have a conjugate seesaw (the equilibrium arrows), what would the pH of the solution be? Are we able to tell, or do we need the kA and kB values to determine this?

Shanzey

If you have a reaction between a strong acid and a strong base, why does that result in a neutral pH? In addition, why does a reaction between a strong acid and a weak base make the solution acidic, and why does a reaction between a strong base and a weak acid make the solution basic?

Shanzey

Why is it that a Bronsted acid/base is a Lewis acid/base, but a Lewis acid/base is not always a Bronsted acid/base?

Shanzey

When talking about EDTA, would you say that it is hexadentate or polydentate? Can you use polydentate to describe anything that is not monodentate?

Shanzey

In lecture, Dr. Lavelle said that a stronger acid would have a lower pkA. Is this trend the same for kA, or is kA different from pkA? Also, is this true for bases, too?

Shanzey

How are we able to compare strengths between two different acids or bases? For instance, how are we able to tell whether acetic acid (CH3COOH) is a stronger/weaker acid than trichloroacetic acid (C2HCl3O2)? Are we able to tell based off of the electronegativities of the atoms within each compound?

Shanzey

What does an equilibrium constant (kA) mean? Also, is there a difference between kA and pkA? In addition, when do we know to use this formula in a given problem? Are there any instances of it in the homework?

Shanzey

How are we able to tell that As2O3 and Bi2O3 are amphoteric compounds? I drew the Lewis structure for the compound, but I do not understand how we can tell that they possess both acidic and basic abilities.

Shanzey

For part b, how are you able to tell that BF3 is a Lewis acid? Where would the newly accepted electrons go on the Lewis structure? Would the new bond be formed with boron or with fluorine?

Shanzey

How are you able to determine if something can be an amphoteric compound without knowing the chemical reaction equation? Does it have to do with the number of hydrogen atoms attached to the molecule?

Shanzey

I feel like the term "coordination compound" has been used a lot throughout lecture, but I am still a bit confused as to what the actual definition fo a coordination compound is. Is it a complex formed between a ligand and a transition metal?

Shanzey

Are Bronsted acids different from Lewis acids because they deal with accepting protons, rather than electrons?

Shanzey

One of the lecture slides said that an unhybridized 2p orbital is perpendicular to the in plane sp2 orbitals, but I am not really sure what this means and how to visualize it.

Shanzey

In one of the UA sessions, the UA mentioned that sigma bonds require more energy to break than pi bonds. Why is that?

Shanzey

During lecture Dr. Lavelle said that everything inside the square brackets is in the coordination sphere. How are you able to tell if something is not in the coordination sphere (not inside the brackets)?

Shanzey

For part a, how do we know that the bond angles for H-C-H and H-C-C are 120 degrees? Is it because each central atom has a trigonal planar shape, and the bond angle for trigonal planar is 120 degrees?

Shanzey

Does having a lone pair on the central atom decrease the bond angles of the other attached atoms?

Shanzey

How do we know that the shape of I3- is linear and not bent? Is it because of lone pair-lone pair repulsion that causes the shape to be linear (to reduce repulsion)?

Shanzey

For part c of 3f.19, how do we know that CH3(CH2)CH3 is rod-shaped, while C(CH3)4 is spherical, since they have the same number of carbons and hydrogens? Is it because of the notation of how the molecular formulas are given?

Shanzey

For part c of question 3F.3, why does CH2Cl2 have dipole-dipole interactions? If we were to draw the two chlorine atoms opposite from each other, wouldn't the dipoles cancel out, making it nonpolar?

Shanzey

I believe that we put the lone pairs across from each other in order to minimize electron repulsion for octahedral shapes. For instance, Dr. Lavelle used the example of XeF4 in lecture and placed the lone pairs opposite from each other because that is the shape with the least amount of repulsion for...

Shanzey

How does polarizability affect intermolecular forces? Do things with high polarizability form stronger bonds?

Shanzey

How are we able to determine how strong each of the bonds are relative to one another?

Shanzey

How do bonds affect the states of matter (whether it's a solid, liquid, or gas) for a molecule?

Shanzey

Are these alpha values for polarizability given, or will we have to calculate them ourselves?

Shanzey

Dipole arrows are drawn on Lewis structures and point towards the more electronegative atom, since they pull electrons towards them. This is why in water the dipole arrows are drawn going from hydrogen (low electronegativity) towards oxygen (higher electronegativity). Due to this pulling of electron...

Shanzey

For resonance structures, is the bond length an average of the experimental bond lengths because of delocalization?

Shanzey

Debora Fernandez Clemente_ 4H wrote:I know understand what a coordinate covalent bond is but, how did you know what compound was a base or an acid?

A Lewis acid accepts electrons, while the Lewis base donates electrons, usually as lone pairs.

Shanzey

If an atom has high polarizability, does that mean that that the atom pulls the electrons, or are the electrons being pulled from it? In addition, what are the trends for polarizability? Does it follow the same trend as ionization energy, electronegativity, and electron affinity?

Shanzey

When drawing a radical, do we put the radical on the atom that is less electronegative, since it does not pull electrons towards it as strongly?

Shanzey

When labeling the dipole moment on a Lewis structure, how are we able to tell if the structure is polar or nonpolar? How are we able to tell if there is no net dipole?

Shanzey

During lecture, Dr. Lavelle mentioned expanded octets, but I am unsure of what he meant by that. What is an expanded octet, and can atoms that follow the octet rule have expanded octets (or is that a violation of the octet rule)?

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